Transformerdesignconsideration forFull Bridge PhaseShift

1 TransformerdesignconsiderationforFull Bridge PhaseShiftJos M. MolinaIEEE APEC 2020: PSMA IndustrySessionDesignof MagneticsforDifferentCircuitTopologies17 March2020, New Orleans, USAAre analyticalmodelstheoptimalpathforPowerEl ectronics?PAGE 3 Full- Bridge Phase Shift (FBPS) The main features of the FBPS power converter are: 4 switches + (2 or 4) diodes Galvanic Isolation Typical topology for power levels >300W High efficiency Suitable as a Voltage or current sourceSome of the relevant publications in the literature related with this converter before becoming an industry standardPAGE 4 FBPS relevant publicationsSabate 90 Redl 90 ZVS conditions Effective duty cycle Clamping Diode LextJ. A. Sabate, V. Vlatkovic, R. B. Ridley and F. C. Lee, "High-voltage, high-power, ZVS, full- Bridge PWM converteremployingan activesnubber," [Proceedings] APEC '91: SixthAnnualAppliedPower ElectronicsConference and Exhibition, Dallas, TX, USA, 1991, pp.

2 158-163R. Redl, N. O. Sokaland L. Balogh, "A novel soft-switchingfull- Bridge DC/DC converter: Analysis, designconsiderations, and experimental resultsat kW, 100 kHz," 21st AnnualIEEE ConferenceonPowerElectronicsSpecialists, San Antonio, TX, USA, 1990, pp. 5 FBPS relevant publicationsAfter the researchers have make their publications, industry started to create design industry has leathered the publication of app notes for Phase Shift Full Bridge converter using their chips. FBPS intervals1212 Javier Torres PROTOTIPADO Y CONTROL DE UN CONVERTIDOR CC-CC PARA ALIMENTAR UN RADAR ELECTR NICO FBPS intervals3434 Javier Torres PROTOTIPADO Y CONTROL DE UN CONVERTIDOR CC-CC PARA ALIMENTAR UN RADAR ELECTR NICO FBPS intervals5656 Javier Torres PROTOTIPADO Y CONTROL DE UN CONVERTIDOR CC-CC PARA ALIMENTAR UN RADAR ELECTR NICO PAGE 9 Design goalsLOW EMILOWCOSTLOW VOLUMEEFFICIENCYE ffective Duty CycleHigh dv/dtOscillationsNumber of MagneticsZVSKey parameters of the designEffective Duty CycleHigh dv/dtOscillationsNumber of MagneticsZVS2 XKey parameters of the designPAGE 12 High dV/dT Due to the High dv/dt in the nodes A and B, the layout connections should be designed to minimize the distances as much as possible.

3 Additionally, the high dI/dt during the transients affects the losses in the magnetics. Classical steinmetzequations are not suitable and the modified steimetzor other models could be used. PAGE 13 Duty cycle losses Due to the leakage inductance, there is a loss of the effective duty cycle in the transformer. This effect should be considered in the turns ratio calculations considering the Llkprediction (or goal)PAGE 14 Oscillations It s very common to find oscillations in the secondary diodes due to the resonance between Llkand the parasitic capacitance of the diodesPAGE 15 ZVS in FBPSA chieving ZVS in the Full- Bridge Phase Shift is almost prevents: High EMI noise Switching losses Semiconductor failure rate increase The main parameters that have an influencein achieving ZVS are: Cossfrom the MOSFET Transformer parasitics Cin Lmag 16 ZVS conditionsInthephenomenonfordischargingt heparasiticcapacitances,theLLkiskeyasexp lainedby[Sabate 90].

4 IftheenergyintheLLkisenoughduringthedead timefordischargingthecapacitor, turn ON with VDS=0 EcELkELoadZVS with additional inductanceInthepublicationofRichardRedl[ 90],heintroducesanadditional commutating inductorwhichextendstheZVSrange. "#+ "%> %PAGE 17 ZVS with the Magnetizing currentForverylightloads,wheretheenergyi ntheLeakageinductanceisverylow, (Lmag, Vin) ismaximumduringthecommutationinstantsJos Mar a Molina Thesis, 2017, ThreePhaseBucktyperectifierintegratedwit hcurrentfedfull Bridge PAGE 18 ZVS considerationsConsiderations during the design: Too much energy stored in the LLk(or external inductance), produce an increment in the conduction losses in every component through a circulating current. For the magnetizing current, the effect is the same. The ideal design will have low magnetizing current, and the leakage inductance integrated in the operation for achieving ZVS without additional 19 Effective Duty CycleHigh dv/dtOscillationsNumber of MagneticsZVSW hich are the key parameters?

5 Phase Shift and PWM modulations force this dV/dt, increasing the noise. Semiconductors should are key elements hereThis effect is mainly produced by the Llk,justified by this equation:ZVS is very recommended for a proper operation of the system. Transformer Llkand Lmare key parametersOscillations between Llkand secondary diodes parasitic capacitance can cause system a key element hereWith accurate estimation of Llk, a commutating additional inductor could be avoidedPAGE 20 PAGE 21 Conclusion: The transformer is a key elementThe importance of the transformer in this converter is huge because is the key element for : Design decisions ( Semiconductors selection, turns ratio) Soft switching Number of magnetics Implementation (Functionality, PCB design) Size (It s the biggest and expensive component) PAGE 22 Transformer parametersThe parameters with high interest in the case of the FBPS (very similar to any case) are: Permeability (for the BH model) Cin Rdc Rac Lmag LLkPAGE 23 Transformer parametersThe parameters with high interest in the case of the FBPS (very similar to any case) are.

6 Permeability (for the BH model) Cin Rdc Rac Lmag LLkLLkis selected for this analysis because its influence in the FBPS and the difficulties to accurately predict his valuePAGE 24 Leakage Inductance (LLk)Leakageinductanceparasiticeffectpro ducedbytheimperfectmagneticcouplingbetwe enthetransformerwindings. Themagneticfluxgeneratedintheprimarywind ingisnevertransferred100% leakage inductance depends basically on:- The winding geometry- The core geometry- Number of turnsPAGE 25 Impact of winding configuration in LLkOne of the ways of playing with this parameter is having different winding strategies. The following configuration strategies provide different coupling resultsVertical windingsHorizontal WindingsInterleavingDoble layer InterleavingPAGE 26 Impact of winding configuration in LLkThe results of leakage inductance for 3 cases with 2 different winding 27 Impact of winding configuration in LLkHorizontal 2 layer to 4 layers interleaved From Llk= uHVertical 2 layers to horizontal 2 layer From Llk = 2 uH Horizontal 2 layer to 3 layers interleaved From Llk =11 uH PAGE 28 How can we predict LLk?

7 And element math methodologies and ai (fre19)CLASSICAL MODELSPAGE 30 LLKI nductanceA lotofmodelscanbefoundinliteratureforcalc ulatingtheleakageinductance. Twoofthemare:CLASSICAL MODEL: Thisisa simple methodforcalculatingtheleakageinductance sinceonlya smallnumberof dimensionsare necessaryrelatedto :Interleavedtransformerconfiguration:a = windingheight(cm)b = windingwidth(cm)c = insulationthickness(cm) Transformerandinductordesignhandbook ,writtenbyColonelWm. T. 31 LLKI nductanceSTEPHENS-BOYAJIANMODEL:Thismode lconsidersthemagnetomotiveforcedistribut ionandrequiresdetailedknowledgeaboutthew indinggeometryforcalculatingtheleakagein ductanceradialandaxialcomponents, component:Radial component:L. M. R. Oliveira and A. J. M. Cardoso, "LeakageInductancesCalculationforPowerTr ansformers InterturnFaultStudies," in IEEE TransactionsonPowerDelivery, vol. 30, no. 3, pp. 1213-1220, June 2015. doi: 32 LLKI nductanceSTEPHENS-BOYAJIANMODEL:Rogowski factor:Magnetomotive force distribution:PAGE 33 LLKI nductanceWhendo weuse eachmodel?

8 MODELWORKSDOES NOT WORKCLASSICAL Simple winding arrangements. Layers with different height. Nonuniform magnetomotive force distributions. High-frequency Complex winding arrangements. Nonuniform magnetomotive-force distributions. Layers with different height. High-frequency 34 LLKI nductanceLeakage inductance comparison in a conventional winding arrangement:Transformer construction: Core shape: PQ40/40 Core material: Ferroxcube3F36 Number turns: 24 / 24 Wire: Round 12 AWG / 12 AWGMODELCASE ACASE BCASE HPAGE 35 LLKI nductanceLeakage inductance comparison in an interleaving winding arrangement:Transformer construction: Core shape: PQ40/40 Core material: Ferroxcube3F36 Number turns: 24 / 24 Wire: Round 12 AWG / 12 AWGMODELCASE ACASE BCASE H980 nH880 nHMATHEMATICAL MODELS -AIDATA SET PAGE 36AI used for predicting LLkAlgorithmTrained modelReal measurementsResults from classic modelsNeural Networks Machine LearningGenetic Algoritjm PAGE 37 Basic example for predicting LLkin a specific range of power and frequencyPower fsw1 kW100 kHzSpace of data.

9 Transformer n=11 kW FBPS & 100 kHz# DataCorePrimary number of turnsPrimary Litz LLKM odel LLK1PQ32 ,2 uH2PQ40 uH7 uHnPQ50/501014-10 uHDATA SET DATA SET PAGE 38 AlgorithmTRAINED MODEL# DataCorePrimary number of turnsPrimary LLKM odel LLK1PQ32 ,2 uH2PQ40 uH7 uH10 uHPQ32/30N1= 16N2=18 LLk=2 uHBasic example for predicting LLkin a specific range of power and frequencyNeural NetworksDESIGN EXAMPLEPAGE 40 FBPS Design ExampleThe design of a FBPS with the parameters of the Table is designed and the steps for the magnetics are as with Deffand input and output voltage range, the turn ratio is transformer is designed with the lower Llk, the avaibleenergy to discharge Cossis are selected considering maximum Coss, power prototype is built and verifiedPAGE 41 FBPS Design Example Accurate prediction of LLkhelps to have a proper design in the first transformer iteration. ZVS is achieved and semiconductors are used without heatsink 95% of efficiency is achieved at 500 WPAGE 42 ConclusionsThe transformer is the key element in the Full- Bridge performance Leakage inductance is one of the parameters with more impactActual techniques for estimating Leakage inductance are: Not accurate Slow Not scalable to different casesArtificial Intelligence methods allows to estimate accurate leakage inductance in seconds.

10 PAGE 43 What if we extend the AI to the rest of the parameters?AI can complement classical models for a better futurePAGE 44 THANK YOUQ&A